clarified compiler options: show relevant warnings;

--- a/etc/settings	Thu Mar 04 22:01:53 2021 +0100
+++ b/etc/settings	Thu Mar 04 22:02:44 2021 +0100
@@ -16,7 +16,7 @@
 
 ISABELLE_TOOL_JAVA_OPTIONS="-Djava.awt.headless=true -Xms512m -Xmx4g -Xss16m"
 
-ISABELLE_SCALAC_OPTIONS="-encoding UTF-8 -nowarn -target:11 -J-Xms512m -J-Xmx4g -J-Xss16m"
+ISABELLE_SCALAC_OPTIONS="-encoding UTF-8 -Wconf:cat=other-match-analysis:silent -feature -deprecation -target:11 -J-Xms512m -J-Xmx4g -J-Xss16m"
 
 classpath "$ISABELLE_HOME/lib/classes/Pure.jar"